Fluid bed granulation apparatus

ABSTRACT

A nozzle for distributor devices of granule&#39;s growth liquid substance in fluid bed granulators, is distinguished by the fact that it comprises a first duct ( 2 ), with substantially rectilinear axis (A) and with a predetermined diameter, which duct has an end portion ( 3 ) including a supply opening ( 4 ) and made of at least two subsequent segments, a first cone-shaped segment ( 5 ) converging on the axis (A) and a further cone-shaped segment ( 7 ) diverging from the axis (A) and ending in the supply opening ( 4 ), a second duct ( 8 ) extending co-axially inside the first duct ( 2 ), with which it forms an annular space ( 9 ), the second duct ( 8 ) having a supply end ( 10 ) extended inside the first cone-shaped segment ( 5 ) of the first duct ( 2 ).

FIELD OF APPLICATION

[0001] In its most general aspect, the present invention relates to anapparatus for fluid bed granulation processes where granules of a chosensubstance are obtained through continuous growth (of both volume andmass) of granules and seeds of that substance suspended in a fluid bed,by means of a suitable growth substance in the fluid state, continuouslyfed in said fluid bed.

[0002] Particularly, this invention concerns a granulation apparatuscomprising a container, wherein a fluid bed of seeds and granules of thechosen substance to be granulated is obtained, a device for feedingcontinuously said seeds in said fluid bed, a fluidification and supportsystem of the fluid bed and at least a distributor of a flow of thegrowth liquid, comprising a plurality of nozzles for supplying saidliquid substance in the atomized form.

[0003] More particularly, this invention relates to a supplying nozzlefor the granule-growth liquid substance, usable for granulationapparatus of the above kind.

[0004] In the following description and attached claims, such apparatuswill be generally addressed as granulator, while the expression:“granule's seed of a chosen substance”, is generally meant to indicateparticles of the substance to be granulated having dimensions equal orless than about 1,5 mm in diameter. Furthermore, to simplify, the term“seeds” will be used to indicate the granule's seeds.

PRIOR ART

[0005] It's known that to reach a good granulation outcome (prearrangedgranule's dimension, shape and mass) with a fluid bed process of theabove type, a good “wetting” of both the seeds and the growing granulesby the growth liquid is required. And, to this end, the growth liquidmust be fed to the fluid bed in the form of the least possible droplets,certainly less than the seeds and the growing granules, which saiddroplets are to get in touch with. That's to allow, as for example withthe urea, the evaporation of water or different solvent contained in thegrowth liquid (solution of urea), in the fastest and most completepossible way, so as to obtain a high purity final product (granules).

[0006] From this point of view, the dimension of the growth liquiddroplets is so crucial that it's very advantageous, if not necessary, tofeed said growth liquid in the so-called “atomized” form. In thiscondition, actually, the growth liquid is able to get in touch one byone with all the seeds or granules suspended in the fluid bed, and towet evenly and in an optimal way their whole surface.

[0007] In order to atomize the growth liquid substance, the prior artgranulators and, more specifically, their growth liquid supplyingdevices, make use of specific atomizing nozzles fed with said liquid andat the same time with large amounts of air (or other suitable gas) athigh speed. Such speed is, for example comprised between 150 m/s and 300m/s.

[0008] But, although largely used and being advantageous under somepoints of view, the use of the atomizing nozzle of the above mentionedtype causes known drawbacks not yet overcame in the fluid bedgranulation processes of the prior art. Actually, the need to work withlarge amounts of air (or other gas) at high speed prevents a control ofthe granule growth inside the fluid bed and, consequently, leads to theinability to control the final product granulometry betweenpredetermined limited values. This entails expensive classification andscreening operations of the produced granules, the recovery of granulesof unacceptable size (too big or too little), and their recycle upstreamto the granulation process.

SUMMARY OF THE INVENTION

[0009] The problem underlying the present invention is to devise and tomake available a nozzle for distribution devices of growth liquidsubstance in fluid bed granulators, having structural and functionalfeatures such as to allow to obtain said growth liquid substance, first,available in a substantially atomized form and, second, supplied with solow speeds as to overcome the drawbacks linked to the prior art.

[0010] This problem is solved, according to the present invention, by anozzle of the above-mentioned type, characterized by the fact that itcomprises a first duct, with substantially rectilinear axis and with apredetermined diameter, which duct has an end portion including a supplyopening and made of at least two subsequent segments, a firstcone-shaped segment converging on said axis and a further cone-shapedsegment diverging from said axis and ending in said supply opening, asecond duct extending co-axially inside said first duct, with which itforms an annular space, said second duct having a supply end extendedinside said first cone-shaped segment of said first duct.

[0011] As it will be seen in more details in the following description,thanks to such flared cone-shaped segment ending in the supply openingof said first duct, it is possible to obtain easily and effectively adrastic slowing down of the supplying speed of the air (or other gas)flow comprising the atomized growth substance and, as a result, it ispossible to feed said flow with a such low speed inside the fluid bedprovided with one or more nozzles of the present invention.

[0012] In this way, granule's growth inside the fluid bed isadvantageously controlled and, consequently, the final product'sgranulometry.

[0013] Indeed, the low feeding speed allows to limit the final productgranulometry inside a predetermined range of values, which is muchnarrower if compared to the prior art. This because it is surprisinglypossible to control the seeds and granules whirling motion inside thefluid bed granulator, and therefore to control their growth.

[0014] The advantages and the features of the invention will be bettershown from the description of an illustrative and non limitingembodiment of the invention, made hereinafter with reference to theenclosed drawings

SHORT DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 shows schematically and in longitudinal section a nozzlefor growth liquid distributor devices in fluid bed granulators,according to the present invention.

[0016]FIG. 2 shows schematically and in cross section a fluid bedgranulation apparatus comprising the nozzle of FIG. 1, according to thepresent invention.

DETAILED DESCRIPTION

[0017] With reference to FIG. 1, with 1 a nozzle according to thepresent invention is globally indicated, which is particularly suitablefor supplying a chosen granule's growth liquid substance in fluid bedgranulators.

[0018] Said nozzle comprises a first duct 2, preferably cylindrical,with predetermined diameter and rectilinear axis A; said duct 2 has anend portion 3 including a supply opening 4 and is made of preferablythree subsequent segments. A first cone-shaped segment 5 converging onsaid axis A, a second cylindrical segment 6 and a third cone-shapedsegment 7 diverging from said axis A and ending in said supply opening 4(substantially Venturi-shaped).

[0019] According to a preferred but not limiting embodiment, saidcylindrical segment 6 has a diameter 0.4 times of the predetermineddiameter of said first duct 2, while the cone-shaped segment 5 has aconicity greater than the one of the cone-shaped segment 7. Furthermore,the diameter of the supply opening 4 is in-between the diameter of saidduct 2 and the diameter of said cylindrical segment 6.

[0020] The nozzle of the present invention comprises a second duct 8,co-axially extended inside said first duct 2, with which it forms anannular space 9. Said second duct 8 has, in the example represented byFIG. 1, cone-shaped supply end 10, converging on said axis A andextended inside the first cone-shaped segment 5 of said duct 2.Furthermore, its conicity is lower than the conicity of said cone-shapedsegment 5.

[0021] According to a further embodiment of the present invention, thesecond duct 8 has a supply opening 11 is extended in predeterminedspaced relationship from an end of the first cone-shaped segment 5 offirst duct 2, corresponding to the inlet opening 6 a of the cylindricalsegment 6. Particularly, said spaced relationship is advantageouslychosen so that a narrow neck 9 a is locally formed inside space 9 toaccelerate the flow of a fluid flowing in the space itself.

[0022] A nozzle according to the present invention, during a fluid bedgranulation process, works as follows.

[0023] A continuous flow F of a chosen growth liquid substance is fed induct 8 with a relatively low axial speed, between for example 2 and 10m/s.

[0024] A continuous flow G of a chosen gas, for example air, is fedcontinually into the space 9 with an axial speed, between, for example,20 and 50 m/s.

[0025] The flow G accelerates substantially in the narrow neck 9 a, forexample at a speed of 200-300 m/s and impinges the liquid substance flowF exiting from opening 11, which is so accelerated and atomized.

[0026] In particular, as a consequence of such impingement, many minutedroplets of liquid substance inside the gaseous mass are continuallyformed, with dimensions of about (for instance) 20-120 micron.Practically, a continuous formation of a nebulized liquid/gas mixture isobtained (liquid phase dispersed into the gaseous phase).

[0027] Said mixture becomes advantageously compact inside thecylindrical segment 6, that means a uniform distribution of the growthliquid droplets inside the cross-section of flow F-G is obtained and,subsequently, slows down substantially inside the cone-shaped segment 7,with diverging conicity, to even reach a speed of 30-60 m/s.

[0028] This flow of growth liquid droplets is supplied inside the fluidbed of seeds and growing granules, at a very reduced speed as regards tothat presently imposed by the prior art, with the above-mentionedadvantages.

[0029] Besides, a further advantage of the present invention is thatinside the flared cone-shaped segment 7, the flow pressure increases asa consequence of the speed reduction, allowing to obtain a recovery inkinetics energy and therefore a reduction of the global energyconsumption required for the atomization of the growth liquid substance(compression energy of the atomization air). Such reduction in theenergy consumption can be quantified as a 40-50% reduction as regards tothe energy consumption caused by the prior art nozzles.

[0030] With reference to FIG. 2, a fluid bed granulation apparatus (orgranulator) according to the present invention, globally indicated with12, is very schematically and partially represented.

[0031] In that figure, details structurally and functionally equivalentto those represented in the previous figure will be indicated with thesame reference numbers and will be no further described.

[0032] Granulation apparatus 12 comprises a container 13, wherein afluid bed 14 of seeds and granules of the chosen substance to begranulated is obtained, a device for feeding continuously said seeds insaid fluid bed (duct 15), a fluidification and support system of thefluid bed (perforated bottom 16 and blowing means—not represented sinceconventional—of fluidification air or other gaseous fluid FL) and atleast a distributor device 17 for the granule's growth liquid flow F.The apparatus 12 is also provided of a device (duct 18) for the weirdischarge of the final product.

[0033] Advantageously, distributor device 17 includes one (as in theexample of FIG. 2) or more growth liquid supplying nozzles 1, of thedescribed type with reference to FIG. 1.

[0034] The invention thus conceived may be susceptible to variations andmodifications, all falling within the scope of protection defined in thefollowing claims.

1. Nozzle for distributor devices of granule's growth liquid substancein fluid bed granulators, characterized by the fact that it comprises afirst duct (2), with substantially rectilinear axis (A) and with apredetermined diameter, which duct has an end portion (3) including asupply opening (4) and made of at least two subsequent segments, a firstcone-shaped segment (5) converging on said axis (A) and a furthercone-shaped segment (7) diverging from said axis (A) and ending in saidsupply opening (4), a second duct (8) extending co-axially inside saidfirst duct (2), with which it forms an annular space (9), said secondduct (8) having a supply end (10) extended inside said first cone-shapedsegment (5) of said first duct (2).
 2. Nozzle according to claim 1,characterized by the fact that said end portion (3) comprises threesubsequent segments, a first cone-shaped segment (5) converging on saidaxis (A), a second cylindrical segment (6) and a third cone-shapedsegment (7) diverging from said axis (A) and ending in said supplyopening (4).
 3. Nozzle according to claim 1, characterized by the factthat said cone-shaped segment (5) of said first duct (2) has a conicitygreater than the one of the further cone-shaped segment (7) divergingfrom said axis (A).
 4. Nozzle according to claim 3, characterized by thefact that said supply opening 4 of said further cone-shaped segment (7)has a diameter smaller than the predetermined diameter of said firstduct (2).
 5. Nozzle according to claim 1, characterized by the fact thatsaid second duct (8) has a supply opening (11) extended in predeterminedspaced relationship from an end of said first cone-shaped segment (5) ofthe first duct (2), so as to locally form a flow accelerating narrowneck 9 a inside said space (9).
 6. Fluid bed granulation apparatuscomprising a container (13), wherein a fluid bed (14) of seeds andgranules of the chosen substance to be granulated is obtained, a device(15) for feeding continuously said seeds in said fluid bed, afluidification and support system (16) of the fluid bed and at least adistributor device (17) for a flow of granule's growth liquid substance,characterized by the fact that said distributor device (17) comprisesone ore more supplying nozzles for said liquid substance comprising afirst duct (2), with substantially rectilinear axis (A) and with apredetermined diameter, which duct has an end portion (3) including asupply opening (4) and made of at least two subsequent segments, a firstcone-shaped segment (5) converging on said axis (A) and a furthercone-shaped segment (7) diverging from said axis (A) and ending in saidsupply opening (4), a second duct (8) extending co-axially inside saidfirst duct (2), with which it forms an annular space (9), said secondduct (8) having a supply end (10) extended inside said first cone-shapedsegment (5) of said first duct (2).
 7. Apparatus according to claim 6,characterized by the fact that said end portion (3) comprises threesubsequent segments, a first cone-shaped segment (5) converging on saidaxis (A), a second cylindrical segment (6) and a third cone-shapedsegment (7) diverging from said axis (A) and ending in said supplyopening (4).
 8. Apparatus according to claim 6, characterized by thefact that said cone-shaped segment (5) of said first duct (2) has aconicity greater than the one of the further cone-shaped segment (7)diverging from said axis (A).
 9. Apparatus according to claim 8,characterized by the fact that said supply opening 4 of said furthercone-shaped segment (7) has a diameter smaller than the predetermineddiameter of said first duct (2).
 10. Apparatus according to claim 6,characterized by the fact that said second duct (8) has a supply opening(11) extended in predetermined spaced relationship from an end of saidfirst cone-shaped segment (5) of the first duct (2), so as to locallyform a flow accelerating narrow neck 9 a inside said space (9).